In recent years, coating technology has been rapidly rising in importance. Various coating methods are being developed.
However, a coating method capable of constructing a high density coating film having a thickness of about tens to hundreds of micrometers has not been known.
The document A. Yumoto, F. Hiroki, I. Shiota, N. Niwa, Surface and Coatings Technology, 169-170, 2003, 499 to 503 and the document Atsushi Yumoto, Fujio Hiroki, Ichiro Shiota, Naotake Niwa, Formation of Ti and Al Films by Supersonic Free Jet PVD, The Journal of the Japan Institute of Metals, Vol. 65, No. 7 (2001) pp. 635 to 643 disclose supersonic free jet (SFJ) physical vapor deposition (PVD) apparatuses.
Such an SFJ-PVD apparatus is provided with an evaporation chamber and a film forming chamber.
In the evaporation chamber, an evaporation source material which is set on a hearth which is cooled by water and an electrode which is made of a high melting point metal (specifically tungsten) are provided. The interior of the evaporation chamber is once reduced to a predetermined pressure then the atmosphere is substituted with a predetermined gas atmosphere. Using the evaporation source material as an anode and a high conductive metal which is located at a position which is spaced from the anode with a constant distance as a cathode, a negative voltage and a positive voltage are applied to induce an arc discharge between the two electrodes. Due to this transfer type arc plasma, the evaporation source material is heated and evaporated. In an evaporation chamber made a predetermined gas atmosphere, atoms which are evaporated by heating of the evaporation source material agglomerate with each other whereby fine particles having sizes of the nanometer order (hereinafter referred to as “nanoparticles”) are obtained.
The obtained nanoparticles ride a gas flow induced due to a pressure difference (difference of degree of vacuum) between the evaporation chamber and the film forming chamber so as to be transported through a transport pipe to the film forming chamber. In the film forming chamber, a substrate for film formation is provided.
The gas flow due to the pressure difference is accelerated up to a supersonic speed of about Mach 3.6 by a specially designed supersonic nozzle (Laval nozzle) which is attached to a front end of the transport pipe connected from the evaporation chamber to the film forming chamber. The nanoparticles ride the air current of the supersonic free jet and are accelerated to a high speed and sprayed to the film forming chamber to be deposited on the substrate for film formation.
By using the SFJ-PVD apparatus described above, it becomes possible to construct a high density coating film having tens to hundreds of micrometers of thickness at a low temperature.
Here, the object of forming a film on the surface of the film formation object is the protection of the surface of the film formation object, insulation of the film formation object, and so on. It has been desired that the material for forming the film have characteristics such as excellent heat resistance, chemical stability, and toughness.
Accordingly, in order to improve the above characteristics of the film which is formed on the surface of the film formation object, for example, there is known the physical vapor deposition apparatus disclosed in Japanese Patent Publication (A) No. 2006-111921 wherein first fine particles and second fine particles are produced in two evaporation chambers, are mixed by utilizing an oscillation phenomenon of coaxial impinging jets described in the document Keijiro Yamamoto, Akira Nomoto, Tadao Kawashima, and Nobuaki Nakaji, Oscillation Phenomenon of Coaxial Impinging Jets, Hydraulics and Pneumatics (1975) pp. 68 to 77, and are made to ride on a supersonic gas flow to be made to deposit on the substrate by physical vapor deposition.